Study finds little evidence of health benefits from organic foods

September 3, 2012

You're in the supermarket eyeing a basket of sweet, juicy plums. You reach for the conventionally grown stone fruit, then decide to spring the extra $1/pound for its organic cousin. You figure you've just made the healthier decision by choosing the organic product—but new findings from Stanford University cast some doubt on your thinking.

"There isn't much difference between organic and conventional foods, if you're an adult and making a decision based solely on your health," said Dena Bravata, MD, MS, the senior author of a paper comparing the nutrition of organic and non-organic foods, to be published in the Sept. 4 issue of Annals of Internal Medicine.

A team led by Bravata, a senior affiliate with Stanford's Center for Health Policy, and Crystal Smith-Spangler, MD, MS, an instructor in the school's Division of General Medical Disciplines and a physician-investigator at VA Palo Alto Health Care System, did the most comprehensive meta-analysis to date of existing studies comparing organic and conventional foods. They did not find strong evidence that organic foods are more nutritious or carry fewer health risks than conventional alternatives, though consumption of organic foods can reduce the risk of pesticide exposure.

The popularity of organic products, which are generally grown without synthetic pesticides or fertilizers or routine use of antibiotics or growth hormones, is skyrocketing in the United States. Between 1997 and 2011, U.S. sales of organic foods increased from $3.6 billion to $24.4 billion, and many consumers are willing to pay a premium for these products. Organic foods are often twice as expensive as their conventionally grown counterparts.

Although there is a common perception—perhaps based on price alone—that organic foods are better for you than non-organic ones, it remains an open question as to the health benefits. In fact, the Stanford study stemmed from Bravata's patients asking her again and again about the benefits of organic products. She didn't know how to advise them.

So Bravata, who is also chief medical officer at the health-care transparency company Castlight Health, did a literature search, uncovering what she called a "confusing body of studies, including some that were not very rigorous, appearing in trade publications." There wasn't a comprehensive synthesis of the evidence that included both benefits and harms, she said.

"This was a ripe area in which to do a systematic review," said first author Smith-Spangler, who jumped on board to conduct the meta-analysis with Bravata and other Stanford colleagues.

For their study, the researchers sifted through thousands of papers and identified 237 of the most relevant to analyze. Those included 17 studies (six of which were randomized clinical trials) of populations consuming organic and conventional diets, and 223 studies that compared either the nutrient levels or the bacterial, fungal or pesticide contamination of various products (fruits, vegetables, grains, meats, milk, poultry, and eggs) grown organically and conventionally. There were no long-term studies of health outcomes of people consuming organic versus conventionally produced food; the duration of the studies involving human subjects ranged from two days to two years.

After analyzing the data, the researchers found little significant difference in health benefits between organic and conventional foods. No consistent differences were seen in the vitamin content of organic products, and only one nutrient—phosphorus—was significantly higher in organic versus conventionally grown produce (and the researchers note that because few people have phosphorous deficiency, this has little clinical significance). There was also no difference in protein or fat content between organic and conventional milk, though evidence from a limited number of studies suggested that organic milk may contain significantly higher levels of omega-3 fatty acids.

The researchers were also unable to identify specific fruits and vegetables for which organic appeared the consistently healthier choice, despite running what Bravata called "tons of analyses."

"Some believe that organic food is always healthier and more nutritious," said Smith-Spangler, who is also an instructor of medicine at the School of Medicine. "We were a little surprised that we didn't find that."

The review yielded scant evidence that conventional foods posed greater health risks than organic products. While researchers found that organic produce is 30 percent less likely to be contaminated with pesticides than conventional fruits and vegetables, organic foods are not necessarily 100 percent free of pesticides. What's more, as the researchers noted, the pesticide levels of all foods fell within the allowable safety limits. Two studies of children consuming organic and conventional diets did find lower levels of pesticide residues in the urine of children on organic diets, though the levels of urinary pesticides in both groups of children were below the allowable safety thresholds. Also, organic chicken and pork appeared to reduce exposure to antibiotic-resistant bacteria, but the clinical significance of this is unclear.

As for what the findings mean for consumers, the researchers said their aim is to educate people, not to discourage them from making organic purchases. "If you look beyond health effects, there are plenty of other reasons to buy organic instead of conventional," noted Bravata. She listed taste preferences and concerns about the effects of conventional farming practices on the environment and animal welfare as some of the reasons people choose organic products.

"Our goal was to shed light on what the evidence is," said Smith-Spangler. "This is information that people can use to make their own decisions based on their level of concern about pesticides, their budget and other considerations."

She also said that people should aim for healthier diets overall. She emphasized the importance of eating of fruits and vegetables, "however they are grown," noting that most Americans don't consume the recommended amount.

In discussing limitations of their work, the researchers noted the heterogeneity of the studies they reviewed due to differences in testing methods; physical factors affecting the food, such as weather and soil type; and great variation among organic farming methods. With regard to the latter, there may be specific organic practices (for example, the way that manure fertilizer, a risk for bacterial contamination, is used and handled) that could yield a safer product of higher nutritional quality.

"What I learned is there's a lot of variation between farming practices," said Smith-Spangler. "It appears there are a lot of different factors that are important in predicting nutritional quality and harms."

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14 comments

I don't buy organic for everything, but I do on a number of items. I tend to shop at stores or markets where the price difference is not that great and where most of the organic produce is locally grown. The reason I do this is twofold. First, no matter what these various studies might imply, I am convinced that the pesticide load is lower and the cleanliness of the water used to grow the products I buy is better than that from other sources/countries. I say this because I can walk the fields myself, talk to the people involved, and directly observe how things are being done. Second--and this is my subjective opinion--organic foods for the most part simply taste better. Whether they are more 'nutritious' as nutrition is measured--I can't say. But more satisfying to the palate--definitely. Some time ago I watched 3 movies--Food, Inc., Vegucated, and Forks Over Knives. These convinced me that most chronic diseases can be prevented or reversed through diet. That alone is worth a few $$.

I'm confused. By reducing the risk of pesticide exposure, isn't there a health benefit? If not, why mention it?

I didn't quite understand that, either. They devoted a long paragraph to that point, then seemed to deduce that as long as the pesticide levels in your body are below some fairly arbitrary safe level, we're all good to go. I'm sorry, but given the choice, I choose less toxic chemicals coursing through my bloodstream.

Healthy foods are more expensive than value foods, organic or not. Fruits and veggies are essential to the diet, but they go bad, cost a lot, and are mostly water.

Any food that isn't in a cardboard box in your freezer goes bad. Agreed. Many foods have a high moisture content. Agreed. Fruits and vegetables are most certainly essential to a healthy diet. Agreed. Healthy foods more expensive than 'value' foods? Well, I don't see it that way. I don't eat 'value' (read fast or heavily processed) foods, and spend ~$110/month on groceries. Is that bad?

I know it wasn't the point of this article, but I hope people buy organic food not only for personal benifits but also to help put less strain on the ecosystem, lower animal stress etc. Organic food should be about respecting both the consumers health and the environment. It's Eco Food, not Ego Food.

Focusing strictly on measurable health benefits is a relatively easy analysis to do, but it oversimplifies by implying health is the sole benefit.

What is the total cost to society of various non-organic techniques?. I don't know, but I bet it's much harder to measure. We're constantly discovering new side-effects of modern farming techniques. Diseases evolve, fertilizer pollutes, etc. Each newly discovered side effect increases the cost.

If for no other reason, easy availability of organic food provides a standard against which new types of non-organic food can be measured.

@ wealthychief: They mention it because it can be a factor. Turns out that it isn't, it is below the allowed threshold. Then, by other work, as Neurons_at_work puts it, you are "good to go".

In another article, it is noted that the differences in pesticide uptake can more simply come from using pesticides in or around the family homes. Presumably they haven't screened for effects of organics eating families that can also minimize their own pesticide use.

@ Pattern_chaser: And it isn't news that this probably doesn't happen. Only two studies finds effects, and I hear the claim they don't take care of all possible statistical confounds (see above).

What eating organics meat gives you are less exposure to antibiotic-resistant bacteria, but now you can by cheaper meats that specifically do not use antibiotic for growth purposes.

@ andreas_zita: "Eco Food". I get so tired of this lazy, conceited and erroneous claim. It is well known from recent meta studies that organics puts *more* strain on the ecosystem, as you put it. Except for, surprisingly to me, fruits. These studies were long in coming, since the woo mongers and snake oil salesmen does not want the oversight - they certainly didn't took the initiative to check themselves.

Organic farming is less efficient (well, duh!), so it uses up more land, oil and other resources. Much more, in fact. Organic fruits are okay because the difference is small enough to be acceptable. (But you should still buy ordinary products if you care about the environment.) It is purely a way to make farmers richer.

To be called organic: "Farmers are not allowed to use synthetic pesticides, bioengineered genes (GMOs), petroleum-based fertilizers, and sewage sludge-based fertilizers." - This does not mean they do not use pesticides. I would think that the only point of synthetic pesticides would be to narrow down the effected organisms to a more specific set of pest. Which to me means that the potential pesticides used by organics could be more detrimental than a synthetic one. The no bioengineered genes portion just seems anti-science. Isn't GMOs used to product more/faster food product.

Any food that isn't in a cardboard box in your freezer goes bad. Agreed. Many foods have a high moisture content. Agreed. Fruits and vegetables are most certainly essential to a healthy diet. Agreed. Healthy foods more expensive than 'value' foods? Well, I don't see it that way. I don't eat 'value' (read fast or heavily processed) foods, and spend ~$110/month on groceries. Is that bad?

That is commendable!

A lot of foods which can be kept outside the freezer don't go bad. For instance flours, oils, nuts, and dried fruit. These aren't necessarily unhealthy, just as long as they are in healthy proportions to the other foods you eat.